A sealant is a thin, plastic protective coating applied to the chewing surface of molars, premolars, and any deep grooves, called pits and fissures, of exposed teeth. Studies have proven that properly applied sealants are very effective in protecting the tooth surfaces from cavities. As long as the sealant remains intact, small food particles and bacteria that cause cavities cannot penetrate through or around a sealant. A sealant protects the tooth by sealing deep grooves and pits of teeth forming a smooth, easy to clean surface.
The only catch with dental sealants is that they should be placed within the first year of eruption, to reduce the risk of sealing in early phase decay on a tooth having been exposed to the oral environment for a longer period of time. Sealants can protect teeth from decay for many years, but need to be checked for wear and chipping at your regular dental visit.